Light-emitting diodes (LEDs) are manufactured by forming active regions on a substrate and by depositing various conductive and semiconductive layers on the substrate. The radiative recombination of electron-hole pairs can be used for the generation of electromagnetic radiation (e.g., light) by the electric current in a p-n junction. In a forward-biased p-n junction fabricated from a direct band gap material, such as GaAs or GaN, the recombination of the electron-hole pairs injected into the depletion region causes the emission of electromagnetic radiation. The electromagnetic radiation may be in the visible range or may be in a non-visible range. Different colors of LEDs may be created by using materials with different band gaps. Further, an LED with electromagnetic radiation emitting in a non-visible range may direct the non-visible light towards a phosphor lens or a like material type. When the non-visible light is absorbed by the phosphor, the phosphor emits a visible light.
LEDs are typically manufactured on a sapphire substrate (Al2O3) for Group III-N compound LED structures because the crystal orientation of the sapphire substrate allows the Group III-N compounds to be epitaxially grown on the sapphire substrate. Sapphire substrates, however, are expensive as compared to silicon substrates. Also, sapphire substrates are typically characterized by thermal accumulation due to the low thermal conductivity of sapphire.
Furthermore, LEDs are typically formed on a planar substrate, thereby resulting in a planar LED structure. A planar LED structure limits the amount of light-emitting material that may be placed on a given size of substrate. Furthermore, the planar surfaces allow the light to be waveguided and trapped within the device, resulting in reduction of extraction efficiency. (See Journal of The Electrochemical Society, 153 2 G105-G107 2006.) As a result, the light emitting efficiency of an LED of a given size is restricted.
Attempts have been made to form LEDs having a non-planar surface in an attempt to increase the amount of light-emitting area on a given size of substrate and spoil waveguiding phenomenon. These attempts result in an LED structure in which the top surface of the LED structure is also non-planar. As a result, a planar surface is not available upon which an electrical contact may be formed on the top Group III-N layer.
Accordingly, there is a need for an LED device having an increased light efficiency with a suitable surface upon which an electrical contact may be formed.